We study the organization and changes in organization of membrane components (lipids and proteins), both in the lateral and in the perpendicular direction. (1) We follow the insertion of a protein into a preformed lipid bilayer (either in the form of a planar bilayer or of a lipid vesicle), and study the factors which determine the protein's orientation. We measure electrical properties of Black Lipid Membranes (BLM) to study: (a) mechanisms of ion transport; (b) properties of transport systems isolated from natural cell membranes; (c) mechanisms of cytotoxicity; (d) the effect of the membrane potential on the disposition of membrane proteins. (2) We have developed model systems in which fusion of phosphatidylcholine bilayers is induced by such proteins as tubulin and clathrin. We study this fusion process using an assay involving resonance energy transfer between two fluorophores incorporated into the vesicle bilayer. (3) We observe lateral organization and movement of fluorescently - labelled molecules on cell surfaces by fluorescence microscopy, and assess diffusion coefficients by the technique of fluorescence recovery after photobleaching (FRAP). We study the mechanism by which asymmetry is maintained in epithelia.